Paper pulp coating of coils



July 1, 1952 I G. CAM ILL! ETAL PAPER PULP COATING 0F COILS Filed Sept. 8, 1949 Inventor's;

ieh'no Camilli dFM.Gr a Leo Mul ligan Ci WiHgh heir Atitorne y Patented July 1, 1952 PAPER PULP COATING. or COILS Guglielmo Camilli and Willard F. M. Gray, Pittsfield, and Leo Mulligan, -West Stockbridge, Mass., assignors to General Electric Company, a corporation of New York Application September 8, 1949, Serial No. 114,512 g This invention relates to electrical insulation and more particularly to an improved method of applying an insulating material to an electrical conductor.

In Patent 2,290,671 to Guglielmo Camilli, Raymond J. Hemphill, and Harold S. Endicott, assigned to the'same assignee as thepresent application, there isdisclosed amethod for hydraulically applying insulation to an electrically conductingarticle. In this method, the insulatinfg material, such as paper pulp, which is to be coated on the article to be insulated, is suitably beaten or broken into finely divided particles of proper size and is then mixed with any suitable liquid, such as water. The article to be insulated may be perforated or a suitable screening or liquid-permeable material may be placed around the article, and the article is then immersed in the liquid. The perforations or screening are necessary in order to allow the liquid adjacent the outside surface of the perforated member or screen to pass through the perforations and deposit its suspension on the outside surface of the screen member when a difference of pressure between the liquid inside the perforated member or screenand the liquid surrounding the per forated member or screen is created. If this movement of the liquid takes place at a sufficiently fast rate, the liquid passing through the perforations will deposit its suspension on the outside surface thereof. In this manner, insulation may be hydraulically applied to any suitable member, such as a coil, it being only necessary to use insulating material which, when beaten, will have particles of fibers of sufiiciently large size so that they will not pass through thepermeable wrap the method just described.

Another problem which is encountered when insulating by the hydraulic method described hereinbefore is that of providing suitable ducts for the passage of liquid about the coil inside the screening or permeable wrapping, since satisfactory deposition of the suspended insulating 2 Claims. (01. 154-80) 2 material requires a relatively fast flow of liquid through the screening surrounding the coil.

It is an object of our invention to provide a new and improved method for hydraulically applying insulation to anelectrical conducting member, such as a coil. 1

It is a further object of our invention to provide a method for applying apluralit'y of layers of insulating material hydraulically.

It is a still furtherobjectiof our invention'to provide an improvement over the hydraulic insulating method disclosed in Patent: 2,290,671,

mentioned hereinbefore.

Another object of our inventionis to provide an improved duct system within the screening 'or permeable wrapping about the coil winding in order to promote more rapid fluid flowtherethrough.

In accordance with the objectives hereinbefore outlined, this invention provides a method for applying a plurality of layers of insulating material by a hydraulic method, wherein after one insulating coating has been applied in accordance with the method described in Patent 2,290,- 671, spacer members and a permeable wrapping are applied over the initial coating, and the channel so provided is connected to a vacuum source in order to draw more liquid through the permeable wrapping,'therebycausing the deposition of an additional coating of insulating material.

Also, this invention provides pressboard spacer members between the concentric turns of a disc coil and also between the coil layers comprised of a plurality of such conce'ntric'turns, in order to provideducts for the free flow of liquid after it has passed through the screening or permeable wrapping surrounding the coil.

.The features of this invention which we believe to be novel'are set forth with particularity in the appended claims. "Our inventionitself,

Fig. 2 is' a cross-sectional view along line 2- 2 of Fig. 1; Fig. 3 is a'view of the coil of Figs. 1 and 2 with an additional layer of insulation applied bers used to provide the liquid-flow ducts shown inFigs, 1. 2, and 3.

In the embodiment. illustrated in the drawing,

coil I is annular shaped and comprises a plurality of superposed winding layers II, I8, I9 and 26. Each winding layer is annular shaped and formed by spirally winding a plurality of'insulated conductor turns such as 2, 3, 4 in a radial plane. While in the embodiment shown in the drawing, each conductor 2, 3, 4 is represented as a single conductor 2, 3, 4 could also represent a plurality conductor turn, it will be understoodthat each of successive spirally-wound turns lying in the same radial plane.

posed layers. The winding layers are arranged in two axially-extending sections which are axially separated by a spacer member I comprised of some material such as cardboard or pressboard spirally wound to form agenerally annular figure, shown separately in Fig. 5. The resultant spacer member I is then placed between the two sections of the coil, as will best be seen in Fig. 2.- In order to maintain ducts between the concentric winding turns 2, 3, and 4, corrugated strips 8 made of pressboard or some similar material are placed between these turns. Separate corrugated strips 8 are used on each side of spacer I which, as has been mentioned, is placed between the two winding sections of coil I. corrugated strip 8 is shown in Fig. i. I

A separate view of the A further layer of the cor-rugated strip 8 may be wound around the complete coil assembly, as shown at 9 in Figs. 1 and 2, in order to space the coil assembly from the perforated container or permeable wrapping to be subsequently applied, as will be described hereinafter.

After the coil I has been provided with ducts by means of spacer members I and 8, and spacer 8 has also been wound around the coil assembly, a shown at 9, the entire assembly is then surrounded by a suitable permeable wrapping or perforated container through whichthe treating liquid may pass to cause the deposition of .insulating material.

In the construction illustrated in Fig. 1, a perforated metal shield is used as the means for filtering the liquid. This shield is in the form of asplit ring I6 having connected to it a perforated metal tube I I through which terminal leads 5 and 6 pass. A shield of this type is described in more detail in Patent 2,280,625 to Camilli, assigned to the same assignee as the present application. Perforated metal ring I6 and its associated connected metal tube I I serve the dual function of providing an electrostatic shield for the coil I, and leads 5 and 6, which may be necessary if the coil i operated at a high potential above ground, and also as a filtering member upon which the suspended insulating material may be deposited.

Theshield is connected to one of the leads 5 or 6 by a conductor I2 so that the shield and the lead to which it is connected will have a definite voltage relationship. If this connection is not made, the shield may assume an indefinite voltage which depends upon the electrostatic capacity between the leads and the shield, and also upon the capacity between the shield andground. The shield is formed with a smoothly curved outer surface, with the radius of curvature of each part of the shield being suificient to prevent corona between the coil I and ground.

After the coil I has been provided with suitable ducts by means of spacer members I' and 8, as shown in Figs. '1 through 4, and has been placed 4 in a permeable container, such as the perforated metal shield hereinbefore described, the whole assembly is then placed in a tank filled with liquid having insulating material, such as paper pulp or asbestos, in suspension, and this suspended material is deposited on the coil assembly in accordancewith the previously mentioned Patent 2,290,671 to Camilli, Hemphill, and Endicott, assigned to the same assignee as the present application. As disclosed in the patent just mentioned,

the tube II .is connected to a source of vacuum,

causing a pressure diiferential on the interior and exterior of the coil assembly, thereby causing a flow of water through the permeable container such as the perforated metal shield I0 and through the ducts formed by spacers I and 8. A the water flows through the perforated metal shield I6, it deposits its suspension of insulating material, such as paper pulp or asbestos, on the outer surface of the shield, thereby building up an insulating coating I3 about the shield and winding.

However, a has been stated hereinbefore, onl a relatively thin layer of insulating coating can be built up in this manner, due to the fact that once such a relatively light coat has been deposited, the vacuum suction will not be suificient to draw any more liquid or water through the already deposited coating. cordancewith our-invention, we provide a construction which permits the depositing of thicker layers of insulating material hydraulically than can be obtained using only the method disclosed in the previously-mentioned Patent 2,290,671 to Camilli, Hemphill and Endicott.

Referring to Fig. 3, there i shown the same coil I as that shown in Figs. 1 and 2, having a layer I3 of insulating coating of paper pulp or other similar material applied thereto in accordance with the method hereinbefore described. In order to add another layer of insulating material, we provide a new system of ducts above the first layer I3 of insulating material. As will be seen in Fig. 3, we spirally wind corrugated spacers 8 over layer I3 of insulating material, and over corrugated spacers 6, we wind a layer of some suitable permeable material such as cotton tape I4, for example. The spacers 8 may be cut into short lengths of slightly more than one turn, as shown in Fig. 3, rather than attempting to wind a continuous spiral around the entire circumference of the coil structure. Spacers 8 and cotton tape winding I l are also placed around the neck portion I5 whichprojects from the circular coil assembly, and which contains leads 5 and 6.

In depositing the additional coat of paper pulp or other insulating material, the neck I5 is connected to a vacuum source and the liquid is sucked through the cotton tape I4 and through the ducts formed by spacers 8, into the vacuum line, as was done when the first coat was. deposited. The suspension of paper pulp or other insulating material will be deposited on the cotton tape wrapping and will build up another insulating coat I6. However, just as in the case of the first coat, a point will be reached where the vacuum will not exert sufficient suction to draw any more water through the cotton tape wrapping I4. If it is desired to further increase the thickness of the insulating coating, it will then be necessary to apply another layer of spacers 3 and permeable wrapping I i around the circumference of the coil assembly on top of the second layer of insulation I6 and also around the second layer of insulation on the projecting neck portion I5. This process can be carried on indefinitely, until Therefore, in acthe thickness of the paper pulp coating around the coil has been built up to the desired thickness.

In the event that the coil which is being insulated is for use with low voltages and does not require a thick coating of insulation or the use of a metal shield member I0, as shown in Fig. l, the structure of Fig. 1 may be modified by omitting the metal shield III which is primarily used for electrostatic shielding purposes and is not necessary when the coil is only subjected to low voltages above ground. In the event that the metal shield I i omitted, the first layer of insulating'material would be applied over a wrapping of cotton tape 14, which would be used in place of the metal shield ID as the surface upon which the suspended material would be deposited.

In other words, a layer of cotton tape l4 would be substitutedfor the metal shield In in applying the first layer of insulation, and would serve as the filtering medium for the application of the first layer of insulation in place of the metal shield 10.

It can be seen that our invention. provides an improved method of depositing insulation hydraulically, since we provide an improved duct system for permitting rapid flow of fluid through the coil body itself, and also provide a simple and effective method for increasing the thickness of the insulating coating, where that is desired.

While there have been shown and described particular embodiments of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein all such changes and modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United Statesis:

1. The method of insulating an electrical winda ing of the type having a plurality of superposed bers between successive turns of said winding, wrapping a corrugated spacer member around the outer surface of said winding, afterwards surrounding said winding with a covering permeable to said liquid, then immersing said winding in said liquid having said insulating material in suspension, and creating a difference in the rela-' tive, pressuresinside and outside said permeable covering so that the liquid adjacent the outside surface of said permeable covering will pass therethrough and deposit its suspension on the outside surface of said permeable covering.

2. The method of insulating an electrical winding of the type having a plurality of superposed coaxial winding layers, each of said layers having I a plurality of spirally-wound conductor turn in coaxial winding layers, each of said layers having troducing the beaten material into a liquid, positioning corrugated axially-extending spacer memthe same radially-extending plane, which includes introducing a finely-divided insulating material into a liquid, said liquid holding said insulating material in suspension, positioning corrugated axially-extending spacer members between successive turns of said winding, wrapping a, corrugated spacer member around the outer surface of said winding, afterwards surrounding said winding with a covering permeable to said liquid, then immersing said winding in said liquid having said insulating material in suspension, and creating a difference in the relative pressures inside and outside said permeable covering so that the liquid adjacent the outside surface of said permeable covering will pass therethrough and deposit its suspension on the outside surface of said permeable covering.

' GUGLIELMO CAMILLI. WILLARD F. M. GRAY. LEO MULLIGAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,350,724 Camilli June 6, 1944 2,382,199 Brink Aug. 14, 1945 2,479,400 Pecoroni et al Aug. 16, 1949 

1. THE METHOD OF INSULATING AN ELECTRICAL WINDING OF THE TYPE HAVING A PLURALITY OF SUPERPOSED COAXIAL WINDING LAYERS, EACH OF SAID LAYERS HAVING A PLURALITY OF SPIRALLY-WOUND CONDUCTOR TURNS IN THE SAME RADIALLY-EXTENDING PLANE, WHICH INCLUDES BEATING A SOLID INSULATING MATERIAL INTO BITS, INTRODUCING THE BEATEN MATERIAL INTO A LIQUID, POSITIONING CORRUGATED AXIALLY-EXTENDING SPACER MEMBERS BETWEEN SUCCESSIVE TURNS OF SAID WINDING, WRAPPING A CORRUGATED SPACER MEMBER AROUND THE OUTER SURFACE OF SAID WINDING, AFTERWARDS SURROUNDING SAID WINDING WITH A COVERING PERMEABLE TO SAID LIQUID, THEN IMMERSING SAID WINDING IN SAID LIQUID HAVING SAID INSULATING MATERIAL IN SUSPENSION, AND CREATING A DIFFERENCE IN THE RELATIVE PRESSURES INSIDE AND OUTSIDE SAID PERMEABLE COVERING SO THAT THE LIQUID ADJACENT THE OUTSIDE SURFACE OF SAID PERMEABLE COVERING WILL PASS THERETHROUGH AND DEPOSIT ITS SUSPENSION ON THE OUTSIDE SURFACE OF SAID PERMEABLE COVERING. 